1. Field of the Disclosure
The present disclosure relates to an improved laminated wood flooring for truck trailers and containers. More particularly, the wood flooring is coated with a hotmelt coating to impart superior protection to the flooring. The use of a hotmelt coating allows the production of improved flooring at high manufacturing speed, low-cost and without environmental issues.
2. Discussion of the Background Art
Conventional wood flooring for over-the-road closed van trailers, truck bodies and containers is normally manufactured with hardwoods, such as oak, maple, birch, beech, ash, etc. The green lumber used as a starting material in such manufacture is suitably dried in special drying chambers under controlled conditions. The dried lumber is then sawed into strips of rectangular cross-section and defective portions are eliminated by cross cutting the strips. During the cross-cutting process, “hooks” are formed at the ends of the lumber strips. Alternatively, other shapes such as fingers, bevel, etc., may be incorporated at the strip ends. These shapes are primarily designed to form a connection or joint between ends of strips. The relatively defect-free lumber strips are coated on their vertical sides or edges with an adhesive such as urea-melamine formaldehyde or polyvinyl acetate. The glue coated lumber strips are then assembled on a conveyor by placing them side to side and behind other strips, which were previously assembled. The adhesive is cured by applying heat and pressure to large sections of the assembled lumber strips thus forming a unitary panel. During the assembly of the lumber strips, “strip-end joints” are formed at each end of every strip with hook, finger or bevel ends. These joints are simple mechanical couplings with no significant adhesive bonding. Often times, due to imperfect assembly, a readily visible gap is formed at these strip-end joints, which can be seen from the top and bottom surfaces of the completed laminated wood floor.
The glued laminated wood is cut to a desired length (up to about 60 feet) and width (about 6 to 18 inches) to form floorboards. Most boards are 10 to 13 inches wide, and 43 to 53 feet in length. The boards are then planed to a desired thickness and shiplaps and crusher beads are machined at the longitudinal edges. A shiplap is a rectangular projecting lip running along the length at an edge of a floorboard. Typically, the lip extends along the width of a board by about ⅜″ to ½″ and has about half the thickness of the board. A “top shiplap” has the lip extending from the top half thickness of the board. Similarly, a “bottom shiplap” has the lip at the bottom half of the board. The crusher bead is a small semi-circular projection running along the length on each edge of a board and placed over or below a lip. When the floorboards are assembled in a trailer such that the side edges of corresponding boards are squeezed together, the top and bottom shiplaps of adjacent boards overlap to form a seam at a board or shiplap joint. The shiplap joint between adjacent boards helps to transfer some of the load from one board to its adjacent board. The board joint also helps to prevent the entry of road debris and water into the trailer. The crusher beads provide spacing between adjacent boards and help in preventing buckling of the boards due to expansion on absorption of moisture. A wood putty is applied at the strip-end joints on the top and bottom surfaces of the boards to fill any resident gaps. Finally, the underside and lateral sides of the floor boards are coated with a water-based latex polymeric coating, which is generally referred to as “undercoating” or “board coating” to provide moisture protection. The coating is usually applied by spraying. The finished floorboards are packaged as kits, by stacking one board on top of another, with about eight boards per kit for installation in trailers. Normally, a kit consists of two boards with special edge profiles so that they will fit along the road and curb sides of a trailer. The other boards may be identical in design and they are placed between the road and curb side boards. All the boards are supported by thin-walled cross-members of I, C or hat sections, each having an upper flange, which span the width of the trailer and are regularly spaced along the length of the trailer. Each floor board is secured to the cross-members by screws extending through the thicknesses of the board and the upper flanges of the cross-members.
Hardwood-based laminated wood flooring is popularly used in truck trailers since it offers many advantages. The surface characteristics of hardwoods such as high wear resistance and traction are most desirable. The strength and stiffness of the flooring is important for efficient and safe transfer of the applied loads to the cross-members of the trailer. The shock resistance of wood is useful to withstand any sudden dropping of heavy cargo on the floor. Nail holding capability and ability to absorb small amounts of water, oil or grease without significantly affecting traction are yet additional favorable properties of hardwood flooring.
Although the conventional hardwood flooring has many desirable features, it also suffers from certain disadvantages. For example, water from the roads is known to leak into trailers through the gaps of the strip-end joints that exist in the flooring. The reasons for the water leaks are believed to be the capillary action of the gaps and the tendency of the end grain of wood to absorb water. Although the undercoating is supposed to provide a barrier to the path of water, it may not properly cover larger gaps thus exposing them to moisture. Further, water based latex coating is significantly permeable to water. Wetting and drying cycles can degrade the water based undercoating leading to its cracking and peeling away from the wood. Wood expands on absorption of moisture and shrinks on drying. Continual cycles of expansion and shrinkage of boards lead to delamination of wood strips of the floor.
To alleviate the above-mentioned problems, a fiber reinforced composite wood flooring was designed, tested and refined to be an improvement over conventional wood flooring (U.S. Pat. Nos. 5,928,735; 6,183,824; and 6,179,942). This composite wood flooring consists of conventional laminated wood floorboards with an underlay of fiber reinforced plastic (FRP). The FRP layer is continuously bonded to the underside of each floorboard. The top surface of the composite wood flooring is essentially the same as that of the conventional wood flooring. Since the FRP is impervious to the passage of water, it completely seals the bottom of the floorboards and solves the problem of leaky strip-end joints. The fiber reinforcement improves the mechanical properties of the flooring and therefore the thickness of the laminated wood can be reduced. However, this approach leads to a product that is much more costly than undercoated flooring.
Alternatively, it is possible to bond a water impervious layer (U.S. Pat. Nos. 6,558,765 and 6,555,766) such as a un-filled plastic sheet or film, filled plastic, recycled plastic, parchment paper, sheet metal, melamine laminate, etc., to protect the bottom surface of floor boards. The plastic can be polyethylene, polypropylene, PVC, polyurethane, ABS, PET, PBT, etc. An adhesive including a reactive hotmelt adhesive is well suited to bond these water impervious layers to wood floorboards. However, the use of a water impervious layer can add significant cost to the product, making it more expensive than undercoated flooring. Further, the process of bonding a separate layer to floorboards is technically more sophisticated compared to the spraying of undercoating. The bonding process requires much more expensive machinery and controls. This has been successfully done to manufacture composite wood flooring using FRP for trailers and therefore other substrates can be easily substituted for the FRP (U.S. Pat. No. 6,601,357). However, this is not a low cost approach to improve water resistance of flooring.
Berube, U.S. Pat. No. 6,318,794, deals with a composite floor with fiber reinforcement at the bottom side and a polyurethane coating enveloping the entire outer surface of the floorboard. This patent also discloses a floorboard with anti-slip polyurethane coating with granular constituent on the top side of board. Polyurethane coatings and even epoxy based coatings have been used in the transportation industry for a long time as floor restorers. Essentially, leaks in the flooring of a trailer, which is in service are sealed by applying liquid polymer coatings on the topside of flooring. In these examples, the use of polyurethane and Isocyanate not only involves high cost for these materials, but also takes considerable time to cure the material by cross-linking chemical reaction to form a protective coating. The faster curing polyurethane coating such as UV-coatings are very expensive and cannot be applied as thick coatings or with coloring agents, due to limitations of UV-curing. These materials also pose chemical hazards and need to be handled with tremendous care. As such, these coatings are not used by the trailer flooring producers.
Technologists are constantly trying to find ways to improve moisture resistance of wood flooring. Fouquet, U.S. Pat. No. 5,143,418, describes the use of composite plywood panels as flooring in open platform trailers. The plywood was composed of veneers of wood with a majority of the veneers oriented with the wood grain along the longitudinal direction while the remaining veneers were oriented with the wood grain along the perpendicular direction. The top and bottom surfaces of the plywood panels were overlaid with resin impregnated cellulose sheets for providing moisture and slip resistance. Plywood based flooring is not used in van trailers due to severe structural load conditions arising from the use of lift trucks to move cargo in and out of van trailers. Further, plywood is generally not available in lengths up to 53 feet, which is preferred for trailer flooring.
Scharpf (U.S. Pat. No. 5,509,715) attempts to provide water protection to laminated wood flooring with a film such as the commercially available Tyvek that is impermeable to water, but permeable to water vapor. The film is discontinuously bonded to the underside of laminated wood boards, so that wood is able to release water vapor through the film, if the floor gets wet. In practice, water protection of the flooring from the underside is present as long as the discontinuously bonded film is not damaged by impacting gravel, rocks and road debris. Sometimes condensate water or other water from leaks in the trailer roof or open doors during rain can wet the top side of the floor. This water can enter the gaps of the hook joints or between boards and become trapped by the discontinuously bonded Tyvek undercovering. Over time, such trapped water leads to warping of the wood boards and breaking of floor screws. Therefore, this product has been discontinued by the industry.
Other techniques have been tried by the industry to eliminate water migration through the flooring from the underside. In one such attempt, a large sheet of plastic film was laid between the cross-members and floorboards. The film was wrapped around and stapled to the edges of the road-side and curb-side boards of the trailer. The film was not adhesively bonded to the boards. During road service of trailers with this type of flooring protection, water was found to enter the spaces between the bottom of the boards and the film. Water could come through the tiny openings around the floor screws. Alternatively, water could also enter from the top side of the flooring from leaks in the roof or from the doors being open in wet weather conditions. The trapped water was absorbed by the bottom side of the floorboards leading to swelling, expansion and warping. Due to these performance issues, this product design was also discontinued by the industry.
The goal of the present disclosure is to improve moisture protection of the bottom side of laminated floorboards at comparable cost relative to conventional water-based latex undercoating. Improved moisture protection in this case means that transfer of water in to the wood of the flooring from the bottom side, which side is exposed to road spray, would be significantly lower than that of undercoated flooring. Another objective of the disclosure is the method of manufacturing of the moisture resistant flooring should be as good or better than that of the undercoated flooring in terms of rate of production, simplicity of operation and ability to handle large volumes.
Conventional undercoated wood flooring with undercoating on the bottom side and exposed wood top side are not suitable for use in open platform trailers. This is because the wood top side of flooring is exposed to the environment. The glue bonds of the wood components tend to break down over time when exposed to uv-radiation and moisture. Wood itself will discolor and weaken from such exposure. Due to moisture related problems, conventional laminated flooring is also not washed with water even when used in closed van trailers. Washing of the flooring is useful after transporting certain products like nursery items, agricultural goods and some chemicals, especially, when a spill occurs. For this type of application, it is preferable to use wood flooring with greater degree of moisture protection on the top side.
The present disclosure does not require a costly water impervious layer, such as a plastic layer or FRP to impart moisture protection to floorboards or wood board flooring. It is also not based on conventional coatings, such as epoxy or polyurethane, that are applied as a 1-part or 2-part liquid at ambient temperature, allowed to penetrate the wood and joints and cured to form a hard surface. Further, the present disclosure does not use a conventional water-based or solvent-based polymer coating.
Conventional water-based latex undercoatings are simple to apply, but have several disadvantages. They do not usually bridge the gaps at the strip-end joints of the board. The coating is also not impervious to water spray from the roads. Since water can transfer in to the wood through the coating, the glue bonds between wood components of flooring can be affected over the life of the floor. The complete drying of water-based undercoating is important to prevent blocking or sticking together of the undercoated boards after these boards are stacked and banded together for shipping. Incomplete drying can lead to transfer of coating from the underside of one floorboard to the top face side of another board in contact with the coated side in a stack of boards. Such transfer of coating can not only lead to blocking, but also contaminate the top wood side of flooring.